The present invention relates to arrangements and methods for avoiding rollovers when braking or accelerating motor vehicles, single-track or double-track vehicles such as motorcycles or passenger cars in particular.
In order to avoid or reduce the possibility of rollovers during braking or acceleration, conventional vehicles have design features such as a long wheelbase, a low center of gravity, a balanced axle load distribution or low braking or propulsive power. More recently, however, vehicles having a short wheelbase and a significantly higher center of gravity have become increasingly popular. In such vehicles, there is the danger that a rollover or tipping over on or about the front axle will take place, especially on downhill grades. There is also the danger that a vehicle with rear wheel drive will tip backwards about the rear axle when strongly accelerating or when reaching uphill grades, for example. Such difficulties also occur, for example, in motorcycles or racing cars, drag racing cars in particular. In motorcycles, the avoidance of rollovers during acceleration is entirely dependent on the driving skill of the driver.
A braking force control system for motor vehicles is known from German Published Patent Application No. 21 33 547 in which a sensor is assigned to each wheel for the measurement of the momentary rotational characteristics, the signals of the sensor being processed in an evaluation circuit and compared with specified rotational deceleration, acceleration and/or slip thresholds, the evaluation circuit emitting signals for operation of the inlet and outlet valves assigned to the wheel if the threshold values are exceeded or not met, as a result of which the braking pressure drops, remains constant or increases in order to avoid wheel locking, an additional logical operation being provided in the evaluation circuit in vehicles having a short wheelbase and a high center of gravity which reduces the pressure on the front wheel brakes if a signal indicating road adherence of the rear wheels does not arrive within a specific waiting period. This printed publication deals exclusively with braking force control systems; arrangements for increasing the safety or handling of a vehicle during acceleration are, however, not dealt with. In addition, the disadvantage of such a braking force control system is that it initiates braking force control only after receiving a signal indicating the lack of road adherence. Due to the elasticity of the tires, this can result in delays in initiating braking force control.
An arrangement for the detection of rollovers in vehicles is known from German Published Patent Application No. 196 09 717 in which angular rate sensors measure the angular rate of the vehicle about the yaw axis, the roll axis and the pitch axis, an arrangement being present which signals a rollover event if at least one of the measured angular rate exceeds a specifiable limiting value.
An object of the present invention is to specify arrangements or methods by which such rollovers can be avoided in an effective manner during braking or acceleration.
According to the arrangement of the present invention, a criterion indicating the danger of a rollover can be specified in a simple manner from the determination of the rotational speed difference of at least one front wheel and at least one rear wheel (or the rotational speed difference between the front and rear axle) with a rotational speed difference threshold value and the determination of a wheel acceleration for at least one front wheel and for at least one rear wheel. When a vehicle with rear wheel drive is accelerated, specifically in the event of an impending backwards rollover about the rear axle, the rotational speed of the rear wheels is increased while the rotational speed of the front wheels is reduced simultaneously. When the rotational speed difference threshold value and corresponding acceleration values are reached, control of the vehicle""s propulsion system is triggered (in particular via an anti-spin regulation (ASR)) to reduce the propulsive power, as a result of which an impending backwards rollover can be effectively avoided. A suitable rotational speed difference threshold value can, for example, be determined on the basis of vehicle tests or also by model calculations which are at least based on vehicle geometry. Advantageously, the threshold value describes a state in which no immediate danger of a rollover exists.
According to another arrangement of the present invention, sensors or switches, limit switches, for example, are attached to the vehicle""s front axle. The position of the front axle in relation to the road surface or in relation to the rear axle can be determined in a simple manner via such limit switches so that in this case also the engine control unit can be activated or propulsive power can be reduced, via an ASR system in particular. In principle, two types of limit switches can be used. The first type of limit switch is a discrete limit switch which simply differentiates whether or not the limit position has been reached. As long as the limit position has not been reached, such limit switches do not generate a signal. Only if the limit position is reached is a signal emitted. In addition, limit switches which emit a continuous-value signal can be provided. Such a continuous-value signal can be analyzed as a measure of the position of the sprung mass (vehicle body) in relation to the unsprung mass (wheel, axle components) or of spring travel at a particular moment. The use of such limit switches makes it possible to detect a braking rollover or even an acceleration rollover solely via a limit switch assigned to an axle of the vehicle. In fact, with a limit switch of this type, it is possible to detect the direction of movement of the sprung mass or the magnitude of the rebound rates, i.e., the changes of the spring travels. If a single limit switch is used, the dynamic characteristics of the vehicle must also be taken into account. The use of level sensors, such as those used in connection with headlight leveling control, is also possible as an alternative to limit switches.
According to another arrangement of the present invention, at least one angular rate sensor is provided to detect a rotation of the vehicle about its rear axis. When angular rate sensors are used to detect an impending rollover, the rotational speed about the corresponding vehicle axle is compared with an associated threshold value. Moreover, the rotational speed is integrated over time and thus the angle of rotation about the corresponding vehicle axis is determined. This angle of rotation is also compared with an associated threshold value. If the rotational speed or the angle of rotation are greater than the associated threshold values, the danger of rollover is recognized.
Advantageously, the characterizing features of the devices specified according to the present invention can be combined in any manner. This makes it possible to achieve increased reliability or safety in the avoidance of motor vehicle rollovers during acceleration.
According to another arrangement of the present invention, rollovers during braking can be avoided easily and reliably. During braking, the state of the vehicle at the start of a rollover is characterized by very strong braking action and by the fact that the vehicle begins to tip frontwards about the front axle. As a result, the rotational speed of the rear wheels which, for example, can be acted upon by an ABS/ASR system, drops to zero due to the abrupt loss of the frictional connection. Owing to the elasticity of the tires, however, this loss of frictional connection does not take place at the same time as the actual start of the rollover motion. However, the switches or sensors detecting the movement or the limit position of the unsprung axle components make it possible to initiate a reduction of the braking action appropriate to the situation already with partial or total rebound, i.e., already before the rear wheels lose frictional connection. In particular, ABS/ASR systems can be used for such reduction. Rollovers during acceleration can be avoided in an analogous manner, since the direction of movement of the unsprung components in relation to the sprung components detected by the switches or sensors is merely the opposite.
According to an advantageous embodiment of the arrangement according to the present invention, at least one active speed sensor is provided which is mechanically linked to at least one rear wheel or the rear axle of the vehicle. This makes it possible to detect reliably a loss of frictional connection of the rear wheels which are in particular affected by an ABS or ASR system, via which an effective criterion for the activation of an ABS or ASR system is made available. Such ABS systems can, for example, reduce the braking pressure or braking force in the front wheel brakes until the rear wheels turn again or a control time limiting value is exceeded, thus ensuring that the vehicle, due to its inertia, is no longer in the process of rolling over but rather comes to a complete standstill. This also ensures that the vehicle does not continue to xe2x80x9ccreepxe2x80x9d forward, which would extend the braking distance in a disadvantageous manner. Particularly in combination with the method of the present invention of attaching sensors or switches to determine the limit position of at least one unsprung axle component, the result is a safe and reliable system to avoid motor vehicle rollovers, resulting in a significant increase of vehicle safety.
Advantageously, the arrangement of the present invention for avoiding rollovers during braking has an angular rate sensor and an arrangement to activate the braking control system in the event a predetermined angular rate is reached or exceeded (i.e., at least reached).
The arrangements of the present invention to avoid rollovers during braking can be used with all braking systems, including braking systems operated with non-liquid or non-gaseous transmission media.
It proves to be particularly advantageous that angular rate sensors attached to the rear axle can be used both for the detection of impending rollovers during braking as well as during acceleration.
The arrangements of the present invention for the prevention of rollovers can, as mentioned, be used advantageously in combination with ABS and ASR systems. A corresponding expansion of such ABS or ASR systems can be easily implemented.